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Freiburg, Germany

The Kiepenheuer Institute for Solar Physics is a research institute located in Freiburg, Germany. Its research focuses on the exploration of the Sun and heliosphere. The institute has one solar telescope on the Schauinsland Mountain near Freiburg and, in collaboration with other institutions, uses solar telescopes of the Teide Observatory in Tenerife, Spain. Wikipedia.

Franz M.,Kiepenheuer Institute for Solar Physics
Astronomische Nachrichten | Year: 2012

A precise knowledge of the surface structure of sunspots is essential to construct adequate input models for helioseismic inversion tools. We summarize our recent findings about the velocity and magnetic field in and around sunspots using HINODE observation. To this end we quantize the horizontal and vertical component of the penumbral velocity field at different levels of precision and study the moat flow around sunspot. Furthermore, we find that a significant amount of the penumbral magnetic fields return below the surface within the penumbra. Finally, we explain why the related opposite polarity signals remain hidden in magnetograms constructed from measurements with limited spectral resolution. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Borrero J.M.,Kiepenheuer Institute for Solar Physics | Ichimoto K.,Kyoto University
Living Reviews in Solar Physics | Year: 2011

In this review we give an overview about the current state-of-knowledge of the magnetic field in sunspots from an observational point of view. We start by offering a brief description of tools that are most commonly employed to infer the magnetic field in the solar atmosphere with emphasis in the photosphere of sunspots. We then address separately the global and local magnetic structure of sunspots, focusing on the implications of the current observations for the different sunspots models, energy transport mechanisms, extrapolations of the magnetic field towards the corona, and other issues. Source

Borrero J.M.,Kiepenheuer Institute for Solar Physics | Kobel P.,Max Planck Institute for Solar System Research
Astronomy and Astrophysics | Year: 2011

In the past, spectropolarimetric data from Hinode/SP were employed to infer the distribution of the magnetic field vector in the quiet Sun. While some authors found predominantly horizontal magnetic fields, others favor an isotropic distribution. We investigate whether it is actually possible to accurately retrieve the magnetic field vector in regions with very low polarization signals (e.g. internetwork), employing the FeI line pair at 6300 A. We first perform inversions of the Stokes vector observed with Hinode/SP in the quiet Sun at disk center in order to confirm the distributions retrieved by other authors. We then carry out several Monte-Carlo simulations with synthetic data, with which we show that the observed distribution of the magnetic field vector can be explained in terms of purely vertical (γ = 0°) and weak fields ( β > 20 G), which are misinterpreted by the analysis technique (Stokes inversion code) as being horizontal (γ ≈ 90°) and stronger ( β ≈ 100 G), owing to the effect of the photon noise. This challenges the correctness of previous results, which presented the distributions for the magnetic field vector peaking at γ = 90° and β = 100 G. We propose that an accurate determination of the magnetic field vector can be achieved by decreasing the photon noise to a point where most of the observed profiles posses Stokes Q or U profiles that are above the noise level. Unfortunately, for noise levels as low as 2.8 × 10-4, only 30 % of the observed region with Hinode/SP have sufficiently strong Q or U signals, implying that the magnetic field vector remains unknown in the rest of the internetwork. © 2011 ESO. Source

Staiger J.,Kiepenheuer Institute for Solar Physics
Astronomy and Astrophysics | Year: 2011

Context. Despite longstanding observational efforts, the origins of the chromospheric temperature rise and the coronal heating are still not well understood. There is reason to believe that the limitations of existing observational devices might be contributing to this lack of experimental evidence. Aims. We intended to develop a multiline spectrometer capable of observing velocity fields simultaneously at more height levels of the solar atmosphere than previously possible. System design and handling would be optimized for the 3D-analysis of atmospheric waves and flows. Methods. The number of optical components was kept to a minimum in order to achieve high optical throughput and short scanning times. A new type of bandpass preselection unit was developed. We successfully tested this Fabry-Perot based multiline device at the Vacuum Tower Telescope (VTT). Results. During a proof-of-concept run we were able to observe 16 spectral lines at a cadence of 60 s sustained over several hours. The field of view was 100-by-100 arcsecs. Multiple diagnostic diagrams from closely spaced height levels were derived. Conclusions. A new instrument of this type will be installed permantently at the VTT. We expect to be able to collect new 3D-information about atmospheric waves and flows. © 2011 ESO. Source

Siegel D.M.,Max Planck Institute for Physics | Roth M.,Kiepenheuer Institute for Solar Physics
Astrophysical Journal | Year: 2014

The universe is expected to be permeated by a stochastic background of gravitational radiation of astrophysical and cosmological origin. This background is capable of exciting oscillations in solar-like stars. Here we show that solar-like oscillators can be employed as giant hydrodynamical detectors for such a background in the μHz to mHz frequency range, which has remained essentially unexplored until today. We demonstrate this approach by using high-precision radial velocity data for the Sun to constrain the normalized energy density of the stochastic gravitational-wave background around 0.11 mHz. These results open up the possibility for asteroseismic missions like CoRoT and Kepler to probe fundamental physics. © 2014. The American Astronomical Society. All rights reserved. Source

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